(a) The Field of the Invention
The present invention relates to modacrylic fibers, viz, to fibers constituted by copolymers of acrylonitrile with other comonomers copolymerizable therewith, and wherein acrylonitrile is present in amounts from 50% to 85% inclusive, which possess reduced inflammability and high luster, and to compositions and processes for their manufacture.
The modacrylic fibers to which the invention refers are prepared by copolymerization of acrylonitrile with the other monomers in an organic spinning solvent miscible with water, particularly dimethylformamide (DMF), but possibly other solvents as well, such as dimethylacetamide, dimethylsulphoxide, etc., to form a viscous spinning dope, and subsequent extrusion of the spinning dope into a coagulation bath constituted by water mixed with the spinning solvent.
(b) The Prior Art
It is known to make modacrylic fibers having reduced inflammability by copolimerizing acrylonitrile with vinylidene chloride, and in order to confer to the copolymer the desired dyeing properties, a further comonomer containing at least one sulphonic group is used, the whole according to suitable weight ratios. According to the known ternary copolymerization technique, the sulphonic groups containing comonomer is normally constituted by the sodium salt of allyl- or methallyl- or vinyl- or styrene-sulphonic acid.
It is also known to prepare a copolymer of the said type or more exactly a mixture of copolymers, instead of by direct copolymerization of the three comonomers (acrylonitrile, vinylidene chloride, sulphonated monomer) by a two-phase copolymerization process, comprising e.g. firstly the preparation of a binary acrylonitrile/sulphonated monomer copolymer, then the addition of said binary copolymer to a solution of acrylonitrile and vinylidene monomers in DMF or other solvent, and the copolymerization of the two latter monomers in the presence of the preformed copolymer; the resulting viscous solution being subsequently spun, e.g., in the wet in an aqueous coagulating bath.
In all such process the problem of obtaining a glossy or lustrous fiber arises. To this end it has been proposed (DOS No. 2624081) to add, in a two-phase polymerization process as hereinbefore described, substantial amounts of water (up to 10%--anyway not less than 4-5%) to the spinning dope.